They can also declare a planned departure to constitute a "manifestly unsafe voyage", see section (g) here:
§*177.07***Other unsafe conditions. :: PART 177--CORRECTION OF ESPECIALLY HAZARDOUS CONDITIONS :: CHAPTER I--COAST GUARD, DEPARTMENT OF HOMELAND SECURITY :: Title 33 - Navigation and Navigable Waters :: Code of Federal Regulations :: Regulations :: L
Thing is, while it is tempting to opine that a voyage "was" manifestly unsafe after a casualty, if this very considerable power is used too often, we are looking at the "nanny state" which most mariners hate.
So in my experience the Coast Guard (meaning a District Commander, the decision actually gets all the way to the Admiral) uses this weapon very sparingly, and usually it's the vessel's condition, rather than the captain's planned route or tactics, that triggers such a finding and termination of a voyage. And they are particularly reluctant to tell a skipper who wants to ride a storm out at sea, that he can't.
Would more people live if they declared a voyage manifestly unsafe if there was even a little doubt? Yes. But at what price freedom and 'captain's discretion', which typically (okay, not here I admit) saves many more lives than it costs?